Analog Devices Inc. AD7854LARS

Overview

AD7854LARS from Analog Devices is a 12-bit, 100 kSPS pseudo-differential successive-approximation ADC optimized for low-power operation on single 3 V to 5.5 V supply. It features on-chip 2.5 V reference, self/system calibration, flexible parallel interface (12-bit or byte-mode), and track-and-hold acquisition in 500 ns. Used in battery-powered medical instruments and portable instrumentation where precision, low quiescent power (5.5 mW at 3 V), and unipolar/bipolar input range support are critical.

For engineers reviewing the AD7854LARS datasheet, AD7854LARS pinout, AD7854LARS application, or AD7854LARS equivalent, this page delivers verified technical context, real-world timing and accuracy specs, package mapping to SSOP-28, confirmed pin functions, and two validated alternative parts with documented functional and application-level differences - all grounded in Analog Devices' official AD7854/AD7854L Rev. B datasheet.

Technical Context

The AD7854LARS implements a charge redistribution SAR architecture with integrated track-and-hold, internal 2.5 V reference, and programmable analog input ranges (0 to VREF unipolar or ±VREF/2 bipolar). Its control register enables software-triggered conversion, system calibration, and three power-down modes via PMGT1/PMGT0 bits.

Timing is clock-driven: conversion time = 18 × tCLKIN (max 10 µs at 1.8 MHz CLKIN); BUSY asserts on CONVST falling edge and deasserts after conversion completes. The parallel interface supports 12-bit read/write using HBEN for byte alignment and CS/RD/WR for register access - requiring two 8-bit transfers per 16-bit register write.

Key Specifications

Pinout & Package

AD7854LARS is housed in a 28-lead Small Shrink Outline Package (SSOP), 0.209-inch body width, gull-wing leads, RoHS-compliant. Pin pitch is 0.025 inch (0.635 mm).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 12-bit, low-power, parallel-interface ADC applications.

Compared with AD7854AR, AD7854LARS trades speed for 63% lower active power and adds automatic power-down - critical for battery longevity. Versus ADS7822U, AD7854LARS provides integrated reference, calibration, and parallel interface but occupies larger board area and requires more control lines.

Availability

AD7854LARS is available at Aetrix Electronics and suitable for portable medical instrumentation, battery-powered data loggers, industrial field transmitters, and pen-based computing interfaces requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for AD7854LARS includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices, Inc. is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, headquartered in Norwood, MA.

The AD7854/AD7854L product line was designed for precision, low-power data acquisition in portable and embedded systems - emphasizing single-supply operation, integrated reference, and software-configurable calibration to reduce system-level design complexity.

FAQ

What is the maximum sampling rate of the AD7854LARS?

The AD7854LARS supports a maximum sampling rate of 100 kSPS, achieved with a 1.8 MHz master clock (CLKIN). Conversion time is fixed at 18 × tCLKIN, resulting in 10 µs max conversion time. This rate is strictly limited by the L-version's internal timing architecture and cannot be increased beyond 100 kSPS even with faster clocks.

Does the AD7854LARS require external reference components?

Yes, the AD7854LARS requires two external capacitors on its reference pins: a 0.1 µF multilayer ceramic capacitor (CREF1) and a 0.01 µF ceramic disc capacitor (CREF2), both connected between their respective pins and AGND. These stabilize the internal 2.5 V reference and ensure accurate DAC operation during calibration and conversion.

How does the AD7854LARS handle bipolar versus unipolar input ranges?

The AD7854LARS selects input range via the AMODE bit in its control register: AMODE = 0 configures unipolar mode (0 to VREF, straight binary coding); AMODE = 1 configures bipolar mode (±VREF/2, twos complement coding). In bipolar mode, AIN(–) must be biased to +VREF/2, and AIN(+) must remain ≥ 0 V - enforced by internal design constraints.

Can the AD7854LARS perform system-level calibration?

Yes, the AD7854LARS supports system calibration through its CALMD and CALSLT bits. When CALMD = 1, the device executes full system calibration - correcting for external sensor, amplifier, and PCB trace errors - using user-provided known reference inputs applied to AIN(+) and AIN(–). Calibration coefficients are stored in on-chip registers and applied automatically during conversion.

What power-down modes are available on the AD7854LARS?

The AD7854LARS offers three software-controlled power-down modes via PMGT1/PMGT0 bits: full power-down (5 µA, CLKIN off), partial power-down (200 µA, CLKIN on), and automatic power-down after conversion (650 µW at 10 kSPS). All modes retain register contents and require no reinitialization upon wake-up.